Flexible retort pouches are gaining popularity around the world as offering greater shelf appeal, greater convenience, and using less material than traditional retort packages, such as metal cans or high barrier rigid plastic containers.
Retort pouches were initially developed as a replacement for metal cans used for military field rations. They have typically been constructed from a flexible multi-layer foil-plastic laminate that is able to withstand post-fill thermal processing for sterilization and provide long shelf life and high durability. However, such packages are generally not suitable for use in a microwave due to the presence of the continuous foil layer, which reflects microwave energy.
More recently, retort pouches that can be used in a microwave oven have been introduced into the marketplace. For example, one package comprises a stand up pouch for rice that uses a non-foil barrier material that is generally transparent to microwave energy. While this type of microwave energy inactive or “passive” package may be acceptable for certain types of comestibles (i.e., food), for example, rice, such packages may have limited utility for other food items because the irregular geometry of the package and the food therein may lead to uneven heating, particularly when the package is a stand up pouch that is heated in the upright position. Additionally, such packages are often too hot to handle after microwave heating. In some commercial embodiments of the above-mentioned package for rice, contoured or wider side seal areas are included near the top of the pouch in an attempt to provide a cooler area for consumers to grasp the hot package after microwave heating.
Thus, there is a need for microwave interactive retort packages that are capable of providing even heating of the food item or items in a microwave oven.